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<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
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  <script>
    let a = 10
    let b = 20
    let c
    c = a
    a = b
    b = c
    console.log(a, b); // 20,10
  </script>
</body>

</html>